G. Brown (George Brown) Goode.

The fisheries and fishery industries of the United States (Volume 1:1) online

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for it can be observed for hours in a fragment cut out of the gill, and if such a fragment be supplied
with fresh sea-water, the motion will continue until it begins to decay. While the Oyster lies
undisturbed on the bottom, with its muscle relaxed and its shell open, the sea-water is drawn ou
to the gills by the action of the cilia, for although each cilium is too small to be seen without a
microscope, they cover the gills in such great numbers that their united action produces quite a
vigorous stream of water, which is drawn through the shell and is then forced through very small
openings on the surfaces of the gills into the water-tubes, inside the gills, and through these tul>es
into the cavity above them, and so out of the shell again. As the stream of water passes through
the gills the blood is aerated by contact with it. The food of the Oyster consists entirely of minute
animal and vegetable organisms and small particles of organized matter. Ordinary sea-water
contains an abundance of this sort of food, which is drawn into the gills with the water, but as the
water strains through the pores into the water-tubes, the food particles nre caught on the surface
of the gills by a layer of adhesive slime which covers all the soft parts of the body. As soon as
they are entangled the cilia strike against them in such a way as to roll or slide them along the
gills toward the mouth. When they reach the anterior ends of the gills they are pushed off and
fall between the lips, and these again are covered with cilia, which carry the particles forward
until they slide into the mouth, which is always wide open and ciliated, so as to draw the food
through the oesophagus into the stomach. Whenever the shell is open these cilia are in action,
and as long as the Oyster is breathing a current of food is sliding into its mouth.

"The cilia and particles of food are too small to be seen without a microscoi>e, but if finely
powdered carmine be sprinkled over the gills of a fresh Oyster, which IMS been carefully opened
and placed in a shallow dish of sea- water, careful observation will show that as soon as the colored
particles touch the gills they begin to slide along with a motion which is quite uniform, but not
much faster than that of the minute-hand of a watch. This slow, steady, gliding motion, without
any visible cause, is a very striking sight, and with a little care the particles may be followed up
to and into the mouth.

"In order to trace the course of the digestive organs, the visceral mass may be split with a
sharp knife or razor. If the split is pretty near the middle of the body, each half will show
sections of the short, folded oasophagus, running upward from the month, and the irregular
stomach, with thick, semi-transparent walls, surrounded by the compact, dark-greenish liver.
Back of the liver and stomach the convoluted intestine will be seen, cut irregularly at several
points by the section.

"There are no accessory organs of reproduction, and the position, form, and general appew-



714 NATURAL HISTORY OF AQUATIC ANIMALS.

ance of the reproductive organ is the same in both sexes. There is no characteristic by which a
male Oyster can be distinguished from a female, without microscopic examination. As the repro-
ductive organ has an opening on each side of the body, it is usually spoken of as double, but in
the adult Oyster it forms one continuous mass, with no trace of a division into halves, and extends
entirely across the body and [against] the bends and folds of the digestive tract." J

(The last of the foregoing statements as to the impossibility of discriminating the sexes with-
out the aid of the microscope is no longer true, though it was true at the time the above was
written. The method of discriminating the sexes discovered by the writer is discussed in another
portion of this sketch of the history of the Oyster.)

The stomach is pretty definitely marked off from the other portions of the digestive tract. It
may be said to be that portion of the latter which is surrounded by the liver. The portion of the
intestine immediately following the short widened region which we regarded as the stomach is the
most spacious portion of the gut, and in it is lodged a very singular organ which has been called
the "crystalline style." This is an opalescent rod of a glass-like transparency and gelatinous
consistence which measures, according to the size of the Oyster, from half an inch up to one and
a half inches in length. Its anterior end is the largest, and in a large specimen measures nearly
an eighth of an inch in diameter, but at its posterior end is scarcely half as thick; both ends are
bluntly rounded. I fell into an error in supposing that this style was lodged in a special pouch
or sac as described in my report to the Maryland commissioner in 1880. The "crystalline style"
really lies in the first portion of the intestine and extends from the pyloric end of the stomach to
the first bend of the intestine, where there is a marked constriction of the alimentary canal. It
appears therefore to be a sort of loose valve in the cavity of the gut; its function may be to
prevent coarse particles of food from passing, or it may in some way assist digestion. In speci-
mens hardened in acid or alcohol this rod is destroyed, or at least disappears, so that I have been
unable to find it. The greater portion of its substance is apparently made up of water.

The peculiar d ouble induplication of the wall of the intestine is described in another place.
The faecal matters are e'xtru ded in the form of a demi-cylinder, with one side excavated in a groove-
like manner. This shape of the fa?cal matters is due to the presence of the double fold. The faces
themselves are composed of extremely fine particles of quartz or sand grains, the tests of diatoms,
organic matters, humus, cellulose, fragments of the chitiuous coverings of some of the minute
worms and articulates, etc., which have been swallowed and digested by the animal. The anus
is situated on the dorsal side of the great adductor muscle where the intestine ends.

The organs of sensation of the Oyster, though not very highly developed, are of sufficient
importance to merit attention. The auditory sense, although I have never been able to dissect out
the auditory vesicles, I am satisfied exists, because one cannot noisily approach an Oyster bank
where the Oysters are feeding without their hearing so that instantly every shell is closed. The
tentacles of the mantle are often extended until their tips reach beyond the edges of the valves.
If the animal in this condition is exposed to a strong light the shadow of the hand passing over it
is a sufficient stimulus to cause it to retract the mantle and tentacles and to close its parted valves.
The mantle incloses, like a curtain, the internal organs of the creature on either side, and lies next
the shell, and, as already stated, secretes and deposits the layers of calcic carbonate composing
the latter. The free edges of the mantle, which are purplish, are garnished with small, highly
sensitive tentacles of the same color. These tentacles are ciliated and serve as organs of touch,
and also appear to be to some extent sensitive to light.

1 W. K. BROOKS: Op. ci.,pp. 8-10.



TIIK INTKKNAI. STIMTTI UK OF Till: (>VSIi:i;. 715

The nervous system of the Oyster is very simple, and, as elsewhere stated, is to some extent
degenerate in character. It is composed of a pair of ganglia or knots of nervous matter, which lie
just over the gullet, and from these a pair of nervous cords pass backward, one on each side, to
join the hinder pair which lie just beneath the adductor muscle. The mantle receives nerve
branches from the hindmost ganglia or knots of nervous matter; these, as their centers, control the
contraction and elongation of the radiating bundles of muscular fibers, as well as those which lie
lengthwise along the margin ; the former contract and withdraw the edges of the mantle from the
margin of the shell, while the latter in contracting tend to crimp or fold its edges. The tentacles
are mainly innervated by fibers emanating from the hindmost ganglia, while the internal organs
are innervated from the head or cephalic ganglia. The hind ganglia also preside over the
contractions of the great adductor muscle. The nerve threads which radiate outward from it to
the tentacles dispatch the warnings when intruders are at hand that it must contract and close
the shells.

211. THE MINUTE ANATOMY OF THE OYSTER.

There is a spacious segmentation cavity developed in the embryo which becomes the
subdivided body-cavity schizocffil of later stages. Between the ectoderm and endoderm the
mesoblastio tissue is developed apparently by proliferation, so that the segmentation or body
cavity becomes in part obliterated. The mesoblast of the embryo formed as above stated is the
tissue from which the mesenchyme or connective tissue of the adult is developed. The blood
channels or canals are developed in the mesenchyme of the adult mesoblast of the embryo.
The large, coarse vesicular connective tissue cells form a sort of trabecular network of pillars and
transverse supports between and around which the sanguineous fluids circulate. The blood
channels or canals are developed directly from the spaces between the columns and their
conjoining masses of connective tissue cells; an exception to this is found only in the structure
of the anterior and posterior aortse, the heart, and branchiocardiac vessels, which have pro|>er
walls lined with endothelial cells. Throughout the greater part of its extent the mesenchymal or
connective tissue is spongy, its cells being built around complex anastomosing spaces for the
blood. There is, therefore, a true schizocoel developed in the Oyster ; it has been formed as the
mesoblastic tissue has grown into the segmentation cavity and subdivided the latter into haemal
canals and spaces. The blood cells originate in all probability in the same way. These are
amoeboid, colorless, and measure about one three-thousandth of an inch in diameter. The vascular
channels have no specialized endothelial walls in the mesenchymal parts of the body.

The adductor muscle of the shell and the radiating muscular bundles running from the
insertion of the former to the edge of the mantle are derived from the mesoblastic cells of the
embryo, the observations of Dr. Horst on this point having, I think, completely set at rest what
was formerly a matter of theory. The radiating muscular bundles pallial muscles of the adult
lie just beneath the epiblast or epithelium on the outer sides of the mantle leaves. These pallial
muscles in the embryo are represented by two sets of dorsal and ventral muscular bundles, the
functions of which are to retract the velum into which they are inserted. The muscular fibers of
the walls of the heart are not striated and decussate in every direction. The inner walls of the
heart are crossed in various directions by muscular bauds or trabeculae, and a more or less
complete muscular septum divides the ventricle in the median liue; the heart is, therefore,
approximately four-chambered.

The mesenchymal or mesoblastic tissues comprise the great bulk of the body of the animal,
and extend out into and form the greatest proportion of the thickness of the mantle, and also



716 NATURAL HISTORY OF AQUATIC ANIMALS.

down into the branchial sacs between their epiblastic or epithelial, ciliated, external walls. It
also forms the principal bulk of the thick vertical, transverse septa which subdivide the branchial
pouches internally, and forms likewise the bulk of the branchial filaments themselves. These
latter are numerous and give the surface of the gills their- furrowed or plaited appearance. The
individual plaits or ridges seen in section are found to be quite complex and to be themselves
eompoundly ribbed and to have chitinous rods embedded in their substance just beneath the
external epithelium. These rods run lengthwise through the substance of the branchial riblets.
The branchial capillaries are excavated in the mesenchymal or connective tissue of the branchial
filaments or tentacles, between which there are numerous openings or ostia for the passage of the
water from the inferior portion of the pallial chamber into the gill cavities in order to effect
respiration. It is difficult, however, to make this arrangement understood without the aid of
figures.

The mesenchyme also gives support to all of the visceral structures, the ultimate secretory
follicles or saccules of the liver being imbedded and supported by it. The same is true of the
generative structures and the intestine. No portion of the walls of the stomach, oesophagus, or
hepatic ducts can be found the walls of which do not lie directly in contact with this mesenchymal
or mesoblastic tissue. It also extends out into and forms the greater proportion of the substance
of the palps or lips of the Oyster, and is very spongy and highly vascular in this region. The
internal or oral surface only of the palps or lips are closely plaited with numerous folds of ciliated
epithelium. These folds may number from one hundred and twenty-five or more. The surface of
the palps in the immediate vicinity of the mouth is not plaited or folded.

The mesenchymal cells are much larger than either the epithelial or endothelial cells, and will
average one five-hundredth of an inch in diameter. They inclose in all cases, both in winter and
summer, a large, irregular nucleus from which a complex network of intracellular granular fibrils
radiate in all directions through the enveloping cellular substance. At one side of the nucleus
there are always one or more accessory bodies, perfectly globular, which complicate the character
of the nucleus in a singular manner. These vesicular, very hygroscopic, meseuchymal or connective
tissue elements are not fat-cells, as has been erroneously supposed by Brooks. Their nuclei are
invariably central and not parietal in position, as in fat-cells. These cells are probably very
hygroscopic, as would appear judging from their singular appearance under the microscope. They
appear to be widely distributed in the molluscous invertebrates; they were originally named
"vesicular connective tissue cells "by the histologist Schaefer. An Oyster may in the summer
season absorb water and swell up so as to fill up almost the whole cavity of the shell, and when
opened it may lose so much blood and water in the course of half an hour that it will have shrunk
to one-tenth of its original bulk. This is a common occurrence, and is explained by the prob-
able hygroscopic character of the connective tissue cells and the spongy nature of the whole
mesenchyme which consists of these elements. This also explains why it is that Oysters may be
much swollen in a short time by osmotic action, when immersed in water of a less specific gravity
than the sea-water from which they were first taken. The process has nothing in common with
what might be called fattening, as we shall see hereafter.

There is an apparent atrophy or wasting away of the mesenchyme of the body-mass and
mantle during the spawning season, with a great concomitant development of the reproductive
follicles or tubules. In winter the reproductive follicles atrophy, when the mesenchyme again
increases in bulk in the body-mass and mantle. It also undergoes another remarkable series
of changes corresponding to summer and winter. In summer it acquires an almost glass-like
transparency, so that the mantle, palps, and superficial portions overlying the viscera become



TOE INTERNAL STRUCTURE OF THE OYSTER. 717

translucent. In this condition, if the reproductive glands are undeveloped, the dark mass of
the liver may be seen through the body walls. Towards the autumn, on the other hand, the
connective tissue cells acquire a milky opacity and great solidity as compared with their watery,
transparent condition in summer. This last condition, which involves the whole mantle, the palps
and superficial portions of the visceral mass, indicates to the oysterman the condition of fatness.
The Oysters in this state are plump ; do not so readily diminish in bulk when removed from the
shell as in summer; but that this change is due to storage of fatty matters I have not yet seen any
evidence of any sort which would amount to proof. There is some oily matter in the Oyster, but
not enough to account for the changes which we have described.

The atrophy of the connective tissue during the summer season would appear to indicate that
the material for the genesis of the reproductive elements was derived from the mesenchyme, by a
direct transformation of its substance in which the generative follicles are imbedded. It is, in
fact, the great development of the mesenchymal substance in the autumn and winter, when the
reproductive function is in abeyance, that constitutes the condition of the animal known to oyster-
men as fatness. These relations illustrate very beautifully a well known physiological principle,
viz, that nutritive processes are very intimately related to the reproductive; they are in fact inter-
dependent.

In summer, when the reproductive organs are gorged with their products, their follicles are
crowded together into contact; in winter, in their atrophied condition, they lie imbedded in the
superficial portion of the mesenchyme of the body-mass, the same as in summer, but are much
less developed, so as to appear in sections like a very open network of strands of very small,
nucleated, incipient embryo cells, the connection of which may be traced into the now collapsed
and internally ciliated branches of the oviducts. All the parts of the reproductive apparatus are
therefore present in winter, but in an undeveloped condition. The oviducts branch and spread
over each side of the body-mass just outside of the stratum of reproductive follicles and imme-
diately beneath the mantle. They do not ramify through the substance of the reproductive organ,
but traverse its surface, the follicles emptying their contents into the ducts by way of openings
upon the inner faces of the latter. The main openings of the oviducts of either side open into the
upper branchial cavity on either side of the hinder and ventral portion of the body-mass just
below the muscle. There is but one opening on either side, notwithstanding the various state-
ments to the contrary.

Embryologically considered, the liver is an endodermal structure, a diverticnlnm of the
stomach. The great bile ducts pass outward from the cavity of the stomach and subdivide again
and again and end blindly in spacious ovoidal hepatic follicles, the simple plicated walls of which
consist of hepatic cells. The function of the liver is in all probability both excretory and secretory,
and takes an all-important share in the processes of digestion. That the function of the liver is
partially excretory is rendered all the more probable from the fact that there is little or no
evidence of the existence of a renal apparatus or organ of Bojanns in the Oyster such as is found
in other mollusks. Dr. Horst looked in vain for a rudiment of this last structure in the embryos
of Ostrea edulis. Transverse sections through those portions of the body where it would most
likely be found, made from both native and foreign examples, exhibit no structure in the least
degree resembling what is regarded as the organ of Bojanus in Unio and Anodonta.

The wall of the intestine, like that of the stomach, is ciliated throughout, and is also of endo-
dermal or hypoblastic origin. Its wall is folded inward along one side in a peculiar way, so that it*
lumen is more or less crescentic in cross-section. This arrangement, together with the very minute
minor folds on its inner surface composed of long, columnar, ciliated epithelial cells, increases the



718 NATURAL HISTOEY OF AQUATIC ANIMALS.

amount of absorbing surface very materially. The internal surface of the stomach is also very
much plicated; but here the folds are both large and conspicuous, with small folds often inter-
vening. There are neither annular nor longitudinal muscular fibers in the wall of the intestiue;
the sole motive force used in the propulsion of the ingested food appears to be exerted by the
ciliary covering which everywhere clothes the internal surface of the alimentary tract from the
mouth to the anus.

It would appear that the intestine makes two complete bends upon itself at a very early stage
of embryonic life, according to the observations of Horst, long before it measures a ninetieth of
an inch in diameter. The development of the liver seems to be at first lateral and somewhat
ventral; an arrangement traces of which may still be noticed in cross-sections of the adult.

The course of the intestine in the adult may be described as follows:

The mouth is a wide opening between the upper median angles of the palpi; so wide, indeed,
that the animal can scarcely be said to have an ossophagus; immediately follows the stomach,
which is seen to have very pronounced folds internally, with a generally transverse direction, but
two of these, which lie in a somewhat ventral position, are a pair of inward-projecting folds which
are themselves plicated. The intestine then follows an oblique course, downward and backward,
when it makes a sharp bend returning beneath the floor of the pericardial space, passing obliquely
upward and forward, somewhat to the right and dorsal of the stomach, when it crosses exactly
over the mouth or very short gullet, passing downward to the left side of the animal, alongside
and a little to the lower side of the stomach, when it again turns upward and passes over the
pericardial space to end in the rectum just over the middle of the adductor muscle. The clusters of
hepatic lobules or follicles dip down into the folds of the walls of the stomach, but the liver does not
follow the course of the intestine proper, which is provided internally with a curious pair of longi-
tudinal and parallel folds, which project into the intestinal cavity and extend from the pyloric end
to very near the anus. The presence of these folds gives to the laecal matters their singular appear-
ance, which are not in the form of a cylinder as they leave the vent, but in the form of a tube with a
part of one side removed. Tracing the course of the intestine by sections is not the proper way;
they can be very easily dissected out for their entire length by means of the scissors and forceps. '

The systemic heart of the Oyster is that organ which serves to propel and redistribute the
colorless blood of the animal through the body for its nourishment, and through the gills that the
blood itself may discharge into the water the poisonous gases with which it is loaded in passing
through the body, and receive a fresh supply of oxygen as fresh supplies of water pass through
the gills. The heart consists of three principal chambers; the upper, largest, whitish and partially
divided by a median septum or partition, is the ventricle, and the two lowermost and smaller,
brownish paired chambers are known as the auricles. These three chambers which comprise the
heart of the Oyster lie in a crescent-shaped space, the pericardial space, just forward of the
adductor muscle. The ventricle is almost globular; its walls are made up of a delicate meshwork
of unstriped muscular fibers, which are so interlaced as to be altogether untraceable. From the
ventricle a great posterior and an anterior aortic vessel arises. These two vessels distribute the
blood to the posterior and anterior portions of the body of the animal, but soon divide into paired
vessels which traverse the mantle on either side both anteriorly and posteriorly, while one great
median branch passes forward over the stomach. The blood is really distributed soon after
leaving the main vessels, especially in the body through the spongy connective tissue spaces, as
already described, and is collected into a great ventral canal from which a large part of it passes
into the gills. From the four gills or branchial pouches the blood flows back to the veutricle



SEX OF THE AMERICAN AND EUROPEAN OYSTERS. 719

through Nix great brauchioeardiac vessels, three of which are arranged on each side; two pairs of
these :m- anterior in position and one pair posterior.

The circulation of the Oyster is quite different in character from that observed in a vertebrated
animal. In the latter the heart pumps the purified blood to und through the gills before it passes
to all parts of the body; in the Oyster, on the other hand, the fresh, pure blood is pumped by the



Online LibraryG. Brown (George Brown) GoodeThe fisheries and fishery industries of the United States (Volume 1:1) → online text (page 119 of 146)